Energy and Power Engineering, 2013, 5, 877-880
doi:10.4236/epe.2013.54B168 Published Online July 2013 (http://www.scirp.org/journal/epe)
The Research on Grounding Protection for 110kV
Resistance Grounding Distribution System
Shan Sun1, Guo Zeng2, X iaozang He2, Yanping Lv1, Xinyi Li1
1Wuhan University, Wuhan, China
2Huangshi Power Supply Company, Huangshi, China
Received January, 2013
ABSTRACT
Using the neutral grounding method by the resistance in 110 kV system, it can limit the voltage sag and short circuit
current when one-phase grounding fault occurred, but it will change the sequence of the network structure and parame-
ters. This paper analyzes the size and distribution of zero sequence voltage and current when one-phase grounding fault
occurred in the 110 kV resistance grounding system, and puts forward the grounding protection configuration setting
principle of this system combining the power supplying characteristics of 110 kV distribution network. In a reforming
substation as an example, the grounding protection of 110 kV lines and transformer have been set and calculated.
Keywords: Neutral Grounding System by Resistance; One-phase Grounding Fault; Zero Sequence Voltage; Zero
Sequence Current; Protection Setting
1. Introduction
With increasing of the industrial automation level, the
sensitivity of the distribution network load increases, and
putting forward higher requirements for the system of
power supply reliability and power quality. It can result
in the decrease of the quality of the products, automatic
production line disorder or interrupted serious conse-
quences when 110 kV neutral grounding system hap-
pened the single phase grounding fault[1]. And single
phase ground fault current is very big, directly affect the
power supply cable’s safety and switch equipment’s se-
lection. Therefore, it is proposed the neutral to the resis-
tance grounding scheme. Voltage drop ability, all kinds
of overvoltage level and current limiting effect of the
system have been deeply researched. And the results
show that if the grounding resistance selection is proper,
under the existing 110 kV electrical equipment insulation
level, it can effectively restrain grounding fault voltage
drop, and obviously improving the quality of power sup-
ply of the distribution network. However, the relay pro-
tection of this kind of grounding way has not been study
in-depth, the paper will explore 110 kV resistance
grounding system grounding protection configuration and
setting calculation principle, basing on the characteristics
of resistance grounding system and the protection of
digital integrated computation ability.
2. Characteristics of Zero Sequence Voltage
and Current
2.1. Zero Sequence Voltage
The system is shown in the Figure 1, when d1 point
happened one-phase grounding fault, the point which
have direct electrical contact with fault point will appear
zero sequence voltage, and the fault point zero sequence
voltage Uf0 is highest, the value is equal to the normal
phase voltage UP.
2.2. Zero Sequence Current
When one-phase grounding fault happened in the neutral
grounding system by resistance, the zero sequence cur-
rent only can flow in the line, transformer and grounding
resistance which direct electrical contact with the fault
point, it can be shown in Figure 2:
The zero sequence current of fault ground is[2]
(0) 0
120 0
3
33
()
PU
f
PR
U
I
RNI
jX XXR



 
 (1)
where, IR

UP/RN is neutral point grounding resistance
current
0f
U
R
U
0
U
R
U
(1)
1
d
Figure 1. The zero sequence voltage distribution in the re-
sistance grounding system.

S. SUN ET AL.
878
As shown in Figure 2, when d1 happened grounding
fault, the zero sequence current through the 1# and 2#
protection are (N-1) IR and IR, the value has nothing to
the fault point location, the zero sequence current of
normal line is very small.
3. Zero Sequence Protection Configuration
and Setting
The typical connection of 110 kV neutral grounding re-
sistance distribution network is as shown in Figure 3.
From the Figure 3, we can learn that the line can be
divided into two types: line-transformer unit and general
line.
3.1. Grounding Fault Protection of
Line-Transformer Unit
The primary protection and back-up protection of this
unit connection respectively use zero sequence current
instantaneous break and zero sequence over-current pro-
tection, the current action value can ensure that it have
enough sensitivity when the grounding fault happened at
the end of the line. Zero sequence quick breaking can 0s
cut off the grounding fault of the line and the trans-
former’s high voltage winding. Because it not need to
cooperate with the low voltage side, the action time of
the zero sequence over-current can set 0.2 - 0.3 s.
But if the fault happened at the low voltage side of the
bus or line, the maximum unbalance current through high
voltage side will cause zero sequence current protection
misoperation, then we need to add the protection of zero
sequence voltage blocking auxiliary criterion, we can set
U0.set=0.5Un(Un is the rated phase voltage)
N
R
N
R
R
I
(1)
R
N
I
R
I
N
R
R
I
(0)
3f
I
110kV
220kV
E
12
(1)
1
d
R
I
Figure 2. The zero sequence current distribution in the re-
sistance grounding system.
1
N
R
N

N
R
110kV
(1)
1
d
(1)
3
d
(1)
2
d
0
T
2
E
1
T
2
T
(1)
4
d
1.0
I
2.0
I
1
E
Figure 3. The typical distribution network of 110 kV neu-
tral grounding resistance.
3.2. Grounding Fault Protection of General Line
The primary protection of the general line must adopt
longitudinal zero sequence current differential protection,
its action value have to hide the maximum imbalance
differential current at the load condition, generally it can
take 0.1 In(In is the rated current of the line). It has the
absolute selective and can quickly remove the grounding
fault. For grounding fault by high resistance, it also has
higher sensitivity.
To prevent losing protection of the line for the longi-
tudinal channel fault, it still need to configuration
back-up protection which does not depend on the channel.
For example, We can choose the line AB in the graph 3
to analysis .
1) Both sides on the line have neutral point grounding
resistance
If the RN of T2 has invested, no matter whether the E2
connect to the grid or not, zero sequence current will
flow through the 2# and 3# protection when grounding
fault happened at line AB. Its nearly back-up protection
can be the zero sequence over-current protection, and it
should ensure adequate sensitivity. Because in the resis-
tance grounding system, generally it can’t limit the action
range of protection, therefore it must be through the time
fit to ensure the back-up protection selectivity.
2) Both sides have power supply, one side have
grounding resistance of the line
If the E2 connect to the grid but T2 has not a grounding
resistance, when grounding fault happened at the line AB,
the 3# protection have no zero sequence current flow. It
should input asymmetric quick-action in succession
function of digital protection: the line happened the
symmetrical short circuit or grounding fault, but the pri-
mary protection can’t action for channel fault, the side
which bigger fault current (2# protection) switch off
three-phase circuit breaker, the offside (3# protection)
measures a phase load current suddenly disappeared and
zero sequence voltage or distance Ⅱ don’t return, so the
3# protection can switch off circuit changer without de-
lay.
3) Only one side has neutral grounding resistance and
power supply
If E2 has no connect to the grid and T2 does not neutral
grounded, so the line AB is a single supply circuit. When
the grounding fault happened at the line, it can remove
the fault by 2# nearly back-up protection when primary
protection can’t action. When the circuit changer refused
to action, the fault can remove by the transformer on the
side which neutral grounded by resistance. As shown in
Figure 3, the zero sequence over-current protection can
be the far back-up protection for 2# protection. For the
side which one side have power supply but no grounding
resistance, it can only use bus zero sequence voltage
protection as the far back-up protection.

S. SUN ET AL. 879
Transformer’s zero sequence current protection should
not only as itself ground fault near back-up, and as the
adjacent element ground fault far back-up [3]. The set-
ting value should cooperation with adjacent element
ground protection backup segment. We should still pay
special attention to the characteristics of the resistance
grounding system: Whether earth fault point located on
the side of the grid which place, each neutral resistance
has IR through. Obviously the current appear only shows
that a ground fault exist, cannot reflect the fault point
location, so the protections of the selective must through
the time fit to complete. Zero sequence flow time setting
is divided into two sections: short time limit which fit
with adjacent element nearly backup action time, as its
ground fault far backup for switching off circuit breaker
of transformer on 110 kV side (for three winding trans-
former). Long time is higher than its short time a , as
transformer internal ground fault backup for switching
off transformer’s each side circuit breaker.
t
4. Grounding Protection Setting Examples
for Resistance Grounding System
A transformation substation as a case, setting the 110kv
system’s grounding protection, the system connection as
shown in Figure 4. Because only in the power supply
side, main transformer’s 110 kV side grounded by a 200
Ω resistance, and cable line was short, so in the condition
of 110 kV line term occurring ground short circuit, zero
sequence current which through the fault line protection
and main transformer 110 kV neutral point is the same
(about IR). For simplifying, it can set each element’s zero
sequence over-current value be the same, and the action
of the selective can be ensured by the stepped.
1) The setting of primary grounding protection of line
l1, l3
l1, l3 are line-transformer unit connection,
.1 .3..
=/ =()/
115/ 31166
0.2 2
s
etsetRsenP Nsen
IIIKURK
A




ⅠⅠ
2) The setting of primary grounding protection of line
l2 l2 is a general line, the current start element setting for:
200
N
R

1
l
2
l
3
l
3
T
2
T
1
T
1101400 /16.5YJSV k
M

1101400 /8YJSV k
M

1101400 /15YJSV k
M

Figure 4. The system of a 110 kV terminal substation.
3
40+40
0.10.110 40.2
3 115
CD n
I
IA 

Ratio braking coefficient k take 0.75; Inflection point
current is 0.7 In
3) the setting of l1, l2, l3 and main transformer ground-
ing back-up protection
The back-up protection of grounding fault for each
line and main transformer uses the zero sequence over-
current protection, the current constant value setting to
the same, are:
.1.2 .3 .T.
115/ 31133
0.2 2.5
===/
=
s
etset setsetR sen
A
IIIIIK

Ⅱ
t1 and t3 are the time limit for the line of l1 and l3, they
should meet with the primary protection:
t1= t3= 0+=0.2s t
The time limit t2 of l2 must cooperate with the back-up
protection of l1:
21 0.2+0.3=0.5tt ts


The zero sequence over-current protection of l2 can be
this line nearly back-up, and also can be used as adjacent
element far back-up.
The time limit tT.1 of main transformer zero sequence
over-current I should be cooperate with the longest time
limit of adjacent element grounding back-up protection:
.1 20.50.30.8 T
ttts


The Ⅱ action time tT. 2 should be cooperate with the I
time limit:
.2 .10.80.31.1 TT
tt ts
5. Conclusions
This paper studies the zero sequence current and voltage
of 110 kV resistance grounding system, the paper puts
forward the grounding protection configuration setting
plan of the system:
1) For line-transformer unit and general line, we
should respectively use zero sequence current instanta-
neous break and zero sequence current differential that
can selectively and rapidly to remove the grounding fault
of the line.
2) For line-transformer unit and general line, the
grounding back-up protection can use zero sequence
over-current protection, the current setting value should
ensure the end of the protection range have higher sensi-
tivity. Because the value generally has no selectivity, the
selectivity of back-up protection can ensured by stepped
time of over-current protection.

S. SUN ET AL.
880
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